A modular 2D fighter with expansive character creation.
Step 1
Choose a body type and modifications- Thinking of P4A characters, Elizabeth couldn't take too many hits and could only deal large damage with combos, but her SP gauge refilled over time. This would be a modification, but taking it would severely hurt other areas of your characters. Light characters are generally faster and have less frames to their attacks, but heavier characters have more room to work with points in stats.
For the example, I'd make a light character with low defense and high attack. I'd possibly throw in a modification where I get a charging move, having this meter full makes certain attacks more powerful and have more effects but depletes the gauge. This weakens my stats, but not too heavily.
Step 2
Choosing a style. Elements such as electricity, and what attacks can do effect-wise. Style is also affected by weapon. Ultimately, style is the most affected by special inputs chosen- nearly all characters have the same base abilities (throws are always the same button combination, for instance) but any inputs can be modified.
Let's say I choose Electricity, which gives me access to things such as stuns and disabling status effects. For inputs, I can have presets of specials- I can choose a wide number of attacks that don't eat the SP gauge at the cost of limited options for SP attacks, or I can have attacks that drain the SP gauge in fourths at the cost of fewer 50SP attacks AND fewer specials that don't eat the SP gauge.
For a weapon, I'll take the Gun. My specials are divided in 4-0SP/2-50SP/1-100SP, plus 1 special from the modification.
My specials are as follows:
88 S - Charge Special
896 (L/M/H) - Discharge (Electricity special, not a projectile. Affected by charge level- if charged, it will last longer and pull the enemy to the attack.)
874 (L/M/H) - Mortar (Anti-air, attack strength determines projectile arc. Affected by charge level- electric effect.)
44 or 66 S - Rush (Low-to-the-ground dash attack, can be chained- inputting other SP commands during Rush activates them when it finishes.)
896 S - Executor (During Rush, grabs enemy after if within range and does a special, extra-damage throw.)
874 S - Target Shooting (During Rush, grabs enemy after if within range and throws into the air. Opens combos well.)
50SP: 47896 (L/M/H) - Burst Railgun (Wide effect projectile storm, useless if enemy is in close proximity in the air (about a 45 degree spread). If charged, projectiles will prevent the enemy from using specials for a small amount of time. If done in the air, the projectiles are aimed downwards at a 45 degree angle.)
50SP: 896896 S - Overcharged Railgun (Wide laser that breaks guards and attack frames. High damage. Can be fired from in the air, and the player will drift down slowly and hit a wider area if fired in the air. Combos, so a single hit dosen't do too much damage, but the whole special does large amounts of damage. If charged, will prevent the enemy from blocking for a short amount of time.)
100SP: 88897 S - Raze the Earth (Instant-kill technique. Activating it causes you to temporarily be unable to use specials, while you charge up for the attack. If you are knocked down, you lose the charge and the SP. After a short time, you will glow blue, and attempting 88 S - Charge will start the attack.
You will launch upwards into the air, leaving a blue streak. Once in the air, you will fire a massive laser from your railgun, moving it in a small arc. Cut to the massive laser covering the entire screen and the enemy OHKO, followed by a special finish screen with a smoldering line left in the Earth's crust.
Step 3
Choosing what your character looks like and their possible palettes. You only get full customization of one palette, and others are preset colors. This has no bearing on your character's abilities, but rather, your character's abilities influence what can be chosen. Let's say I go with a blue and white color scheme with a large cloak covering most of my character and a robotic leg. I can then name my character, save it, and use it in Versus modes as well as upload it to the multiplayer server.
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Multiplayer works like this:
Unranked Free allows you to choose from any character uploaded online.
Unranked Limited allows you to choose from characters with enough upvotes and times used to be thoroughly tested. Exploits and imbalances would have to be fixed through light patches.
Unranked Roster allows you to pick from player-made rosters of characters- either all made by one person, or gathered from downloaded characters- and fight with the set number of characters. You will then be allowed to rank that roster.
Ranked Limited is a ranked version of Unranked Limited.
Ranked Popular is a ranked mode where a number of the most popular characters are available.
Ranked Tournament allows you to choose from characters hand-picked to fill rosters based on all sorts of criteria. Contests to make characters based around concepts and settings to fill rosters could be a single tournament format, along side developer rosters and dev favorites, as well as player-made rosters that reach popularity.